The present invention relates to a web slitter, and more particularly to a slitter for cutting lengthwise a wide and flexible web into a predetermined width.
The web used in the present invention includes generally flexible web-like materials 1.mu. to 1000.mu. in thickness and 0.03 m to 3 m in width made of polyvinyl chloride, polycarbonate, ABS resin, polyethylene terephtalate, cellulose triacetate paper, synthetic paper or the like, and those materials using said web-like materials as a support, to one surface or both surfaces of which is applied a coating film, in layered fashion, for example, such as a photosensitive layer, a magnetic layer, an adhesive layer, a protective layer, a sliding layer, a colored layer, and the like.
A prior art web slitter for cutting (hereinafter referred to as "slitting") lengthwise the aforesaid webs into a predetermined narrow width is generally illustrated in FIGS. 1 and 2. The principal mechanism of this web slitter comprises a plurality of thin-wall circular upper cutting edges 5 located upwardly of a web 1 and supported on a support shaft 2. The upper cutting edges 5 are disposed across said web 1 with a spacing P corresponding to a predetermined slit width and are held and fixed in position by holders 3 each of which has an annulus that project through a central hole of a circular cutting edge and a mating pusher plate 4. The same number of circular lower cutting edges 7 as said upper cutting edges 5 are located downwardly of said web 1 and supported on a support shaft 6 disposed across said web 1 with an outer peripheral width corresponding to said spacing P.
The lower cutting edges 7 are rotated in a clockwise direction as indicated by arrow CW for the purpose of conveying said web 1 in the direction of arrow A while supporting said web 1 to be slitted on the outer peripheral surface thereof. The nose surfaces of said upper cutting edges 5 are rotated in a counter-clockwise direction as indicated by arrow CCW and brought into sliding contact with the corresponding edge surfaces of the lower cutting edges thereby slitting the web 1 passing through the sliding contact point therebetween into a predetermined width.
While the prior art slitter performs satisfactorily under conditions of low speeds and high tensions of the web, it has proved unsatisfactory under high speed production conditions. More specifically, the following disadvantages have developed:
(1) When the conveying speed of the web 1 is increased, a thin layer of air is entrained into the zone of contact between said web 1 and the lower cutting edge 7 as the web 1 moves, resulting in a floating of said web by the entrained air of several microns at most. As a consequence, the web 1 tends to be moved laterally in a zigzag fashion towards the moving direction, and as a result, the web 1 to be slitted is often slitted in a greatly zigzag state with respect to the normal slitting direction.
(2) Particularly, when a web of photographic film is slitted in a greatly zigzag state as previously mentioned, it becomes extremely difficult to accurately make holes in a predetermined position in the proximity of the edge. Further, in the case of video magnetic tape, a regenerative image thereof is materially distorted.
(3) Where the web 1 is thin and the coating film is high in pressure sensitive properties, the above-mentioned zigzag phenomenon is further developed when the tension of the web 1 is set to an extremely low level and therefore, it is necessary to set also the conveying speed of the web 1 to a lower value to prevent occurrence of the air stream as described above. As a consequence, the operating efficiency is considerably reduced.